A. Technical Field
The present invention relates to cellulase compositions producible by Actinomycetes, methods of producing such cellulases and the use of such cellulases. The present invention further relates to the use of the novel cellulase in compositions recognized in the art as advantageously having cellulase added thereto, including, as an additive in a detergent composition, in the treatment of textiles such as cellulose containing fabrics and fibers useful therefor, as an animal feed additive, as a processing aid in baking, in the treatment of pulp and paper and in the treatment of starch for the production of high fructose corn-syrup or ethanol.
B. State of the Art
Cellulases are enzymes which are capable of the hydrolysis of the .beta.-D-glucosidic linkages in celluloses. Cellulolytic enzymes have been traditionally divided into three major classes: endoglucanases, exoglucanases or cellobiohydrolases and .beta.-glucosidases (Knowles, J. et al., (1987), TIBTECH 5, 255-261); and are known to be produced by a large number of bacteria, yeasts and fungi.
Primary among the applications that have been developed for the use of cellulolytic enzymes are those involving degrading (wood) cellulose pulp into sugars for (bio)ethanol production, textile treatments like `stone washing` and `biopolishing`, and in detergent compositions. Thus, cellulases are known to be useful in detergent compositions for removing dirt, i.e. cleaning. For example, Great Britain Application Nos. 2,075,028, 2,095,275 and 2,094,826 illustrate improved cleaning performance when detergents incorporate cellulase. Additionally, Great Britain Application No. 1,358,599 illustrates the use of cellulase in detergents to reduce the harshness of cotton containing fabrics.
Another useful feature of cellulases in the treatment of textiles is their ability to recondition used fabrics by making their colors more vibrant. For example, repeated washing of cotton containing fabrics results in a greyish cast to the fabric which is believed to be due to disrupted and disordered fibrils, sometimes called "pills", caused by mechanical action. This greyish cast is particularly noticeable on colored fabrics. As a consequence, the ability of cellulase to remove the disordered top layer of the fiber and thus improve the overall appearance of the fabric has been of value.
Because detergents, being a primary application of cellulase, operate generally under alkaline conditions there is a strong demand for cellulases which have excellent activity at pH 7-10. Well characterized fungal cellulases, such as those from Humicola insolens and Trichoderma reesei, perform adequately at neutral to low alkaline pH. Further, a number of enzymes that show cellulase activity at high alkaline pH have been isolated from Bacillus and other prokaryotes, see e.g., PCT Publication Nos. WO 96/34092 and WO 96/34108. Thus, both fungal and bacterial cellulases have been investigated thoroughly. However, a third group of cellulases, those isolated from Actinomycetes, have attracted only some attention. Wilson et al., Critical Reviews in Biotechnology, Vol. 12, pp. 45-63 (1992), studied the cellulases produced by the Thermornonospora fusca, Thermonomospora curvata and Microbispora bispora and illustrated that many of these cellulases show broad pH profiles and good temperature stability. Similarly, Nakai et al., Agric. Biol. Chem., Vol. 51, pp. 3061-3065 (1987) and Nakai et al., Gene, Vol. 65, pp. 229-238 (1988) exemplify the alkalitolerant cellulase casA from Streptomyces strain KSM-9 which also possesses an alkaline pH optimum and excellent temperature stability.
Despite knowledge in the art related to many cellulase compositions having desirable properties, including some examples from Actinomycetes, there is a continued need for new cellulases having a varying spectrum of characteristics which are useful in, for example, treating textiles, as a component of detergent compositions, in the treatment of pulp and paper, as an animal feed supplement, as a processing aid for baking and in the conversion of biomass. Applicants have discovered certain cellulases which have such a complement of characteristics and which are useful in such known applications of cellulase.